Two New (3,6)-Connected Frameworks Based on an Unsymmetrical

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Two New (3,6)-Connected Frameworks Based on an Unsymmetrical Tritopic Pyridyldicarboxylate Ligand and Co2 Dimer: Structures, Magnetic, and Sorption Properties Lei Hou, Bin Liu, Li-Na Jia, Lei Wei, Yao-Yu Wang,* and Qi-Zhen Shi Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, College of Chemistry & Materials Science, Northwest University, Xi’an 710069, P. R. China S Supporting Information *

ABSTRACT: By reacting a tritopic ligand 5-(4-carboxyphenyl)nicotinic acid (H2cpna) with Co(NO3)2 under different conditions, two new three-dimensional (3D) frameworks, [Co2(cpna)2(H2O)3]·DMF·9(H2O) (1) and [Co4(cpna)4(H2O)8] (2), have been obtained. They exhibit (3,6)-connected topological nets based on Co2 clusters and Y-shaped trinodal cpna2− linkers. 1 presents a chiral anh net with the right-handed helical channels, while 2 shows an achiral framework with a rtl topology. The whole structures of 1 and 2 are constructed from 2D achiral layers interconnected by triangular cpna2− nodes. Notably, these layers contain two heterochiral vertical and parallel 21 helical chains for 1 and 2, respectively, and those chains are constructed with 4-connected tetrahedral or square planar centers in their respective layers. The magnetic studies indicate that 1 and 2 show antiferromagnetic and weak ferromagnetic exchanges transmitted through μ2-Owater/μ1,3-carboxylate bridges and carboxylate single μ2-O bridges between Co2+ ions in the Co2 dimers, respectively. In addition, 1 displays microporous sorption for N2 and CO2.

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the Y-shaped node tends to generate an rtl net.8 Upon combining the 6-connected [Zn4(μ4-O)(O2CR)6] cluster, the high symmetric trigonal ligand 4,4′,4″-tricarboxytriphenylamine gives rise to the highest symmetric (3,6)-connected net of a pyr topology;9 its longer derivatives impel the formation of a qom net,10 while the lower symmetric tritopic ligand generates an rtl net.11 Therefore, a low-symmetry tritopic linker should allow the formation of more topologically versatile (3,6)-connected frameworks. With this in mind, an unsymmetrical Y-shaped ligand H2cpna (H2cpna = 5-(4-carboxyphenyl)nicotinic acid) (Scheme 1) is used to construct different (3,6)-connected networks. Meanwhile, compared to the considerable research in the field of using carboxylate or pyridyl bridging ligands for building MOFs, a limited number of elongated pyridyl carboxylate ligands have been undertaken. Known examples are mainly related to nicotinate,12 isonicotinate,13 and pyridinedicarboxylate.14 Until now, the pyridyldicarboxylatic acid ligand H2cpna, which can be considered as a combination of nicotinatic acid and benzoic acid or an elongated version of 3,5-pyridyldicarboxylic acid (Scheme 1), has not been investigated in the MOFs area. In this work, two 3D frameworks [Co 2(cpna) 2(H2O)3]·DMF·9(H 2O) (1) and

INTRODUCTION Metal−organic frameworks (MOFs) have currently attracted ever-increasing attention because of their intriguing structural topologies and promising applications as functional materials in magnetism, sorption, separation, catalysis, and drug delivery.1 To achieve the anticipated utilities of MOFs, the net-based methodology has been extensively involved to design and analyze MOFs.2 These MOFs display uninodal or heteronodal nets, which mainly depend on the shapes/configurations of organic and inorganic components. While the enormous uninodal MOFs, such as 3-, 4-, and 6-connected MOFs, have been successfully fabricated, the exploration of higher-dimensional heteronodal networks, such as (3,6)-, (4,6)-, (3,8)-, and (4,8)-connected nets, is not well developed.3 Among those heteronodal networks, the (3,6)-connected nets are particularly significant because the most common [M2(O2CR)n(L)6−n] dimers,4 [M3(μ3-X)(O2CR)6] (X = O2−, OH−)5 trimers, and [M4(μ4-O)(O2CR)6]6 tetranuclear clusters, as well as monometal ions, usually serve as 6-conncted octahedral or trigonalprism nodes, which can be further linked by triangular ligands. According to a survey of the RCSR database, there are at least 20 known examples of (3,6)-connected nets in the literature;7 however, some nets remain unexplored in MOFs though are theoretically anticipated. The (3,6)-connected nets have an intrinsic feature that the topological type is closely related to the shapes, lengths, and symmetries of tritopic organic nodes. For instance, the T-shaped node favorably forms an ant net, but © XXXX American Chemical Society

Received: September 27, 2012 Revised: December 6, 2012

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dx.doi.org/10.1021/cg301413u | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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analyses, and TGA data. Selected crystallographic data and structure refinement results are listed in Table 1.

Scheme 1. Schematic Representation of Relation between H2cpna and Nicotinatic Acid or 3,5-Pyridyldicarboxylic Acid

Table 1. Crystallographic Data and Structural Refinements for 1 and 2a

[Co4(cpna)4(H2O)8] (2) have been constructed by the combination of the trinodal H2 cpna and 6-connected [Co2(O2C)2(μ2-H2O)(H2O)2] or [Co2(O2C)4(H2O)2] dimers, which feature (3,6)-connected anh and rtl nets, respectively. Their magnetic and sorption properties were investigated as well.

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EXPERIMENTAL SECTION

Materials and General Methods. All solvents and starting materials for synthesis were purchased commercially and were used as received. Infrared spectra were obtained in KBr discs on a Nicolet Avatar 360 FTIR spectrometer in the 400−4000 cm−1 region. Elemental analyses of C, H, and N were determined with a PerkinElmer 2400C elemental analyzer. Thermalgravimetric analyses (TGA) were carried out in a nitrogen stream using a Netzsch TG209F3 equipment at a heating rate of 5 °C/min. Powder X-ray diffraction (PXRD) data were recorded on a Bruker D8 ADVANCE X-ray powder diffractometer (Cu Kα, 1.5418 Å). Sorption measurements were performed with an automatic volumetric sorption apparatus (Micrometrics ASAP 2020M). Magnetic properties were tested on a Quantum Design MPMS-XL-7 SQUID magnetometer. Synthesis of [Co2(cpna)2(H2O)3]·DMF·9(H2O) (1). A mixture of Co(NO3)2·6H2O (0.044 g, 0.15 mmol) and H2cpna (0.018 g, 0.075 mmol) in N,N′-dimethylformamide (DMF) (6 mL) and ethanol (1 mL) was stirred at room temperature for 1 h. After filtration, the filtrate stood for about three weeks until the red block crystals of 1 were obtained, which could be collected by filtrating and washing with DMF. The yield was ca. 14 mg (42.0%). Anal. Calcd for C29H45Co2N3O21: C, 39.16; H, 5.10; N, 4.72. Found: C, 39.09; H, 5.15; N, 4.77%. IR (KBr, cm−1): 3390m, 2929w, 1660s, 1618vs, 1558s, 1402vs, 1277w, 1101m, 874m, 785m. Synthesis of [Co4(cpna)4(H2O)8] (2). A mixture of Co(NO3)2·6H2O (0.044 g, 0.15 mmol) and H2cpna (0.018 g, 0.075 mmol) in N,N′-dimethylacetamide DMA (5 mL), ethanol (2 mL), and water (3 mL) was placed in a Teflon-lined stainless steel vessel (15 mL). The vessel was heated at 120 °C for 72 h, and then cooled to room temperature at a rate of 5 °C/h, giving the red prism crystals of 2, which were isolated by washing with ethanol, and dried in vacuo. The yield was ca. 12 mg (47.6%). Anal. Calcd for C52H44Co4N4O24: C, 46.45; H, 3.30; N, 4.17. Found: C, 46.40; H, 3.27; N, 4.20%. IR (KBr, cm−1): 3442(s), 3095(w), 2927(w), 1622(s), 1533(vs), 1396(s), 1340(s), 1269(m), 1167(w), 835(w), 702(m). Crystallography. The diffraction data were collected at 295(2) K with a Bruker AXS Smart Apex diffractometer using ω rotation scans with a scan width of 0.3° and MoKα radiation (λ = 0.71073 Å). The structures were solved by direct methods and refined by full-matrix least-squares refinements based on F2 with the SHELXTL program.15 All non-hydrogen atoms were refined anisotropically with the hydrogen atoms added to their geometrically ideal positions and refined isotropically. The crystals of 1 scattered weakly and only lowangle data could be detected owing to the presence of heavily disordered solvent molecules in the cavities. Thus the SQUEEZE routine of PLATON16 was applied to remove the contributions to the scattering from the solvent molecules. The final formulas were determined by combining single-crystal structures, elemental micro-

a

complex

1

2

formula formula weight T (K) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (g cm−3) μ (mm−1) reflns collected/unique Rint R1a (>2σ/all data) wR2a (>2σ/all data) GOF flack parameter

C26H20Co2N2O11 654.30 295(2) trigonal P3121 11.050(3) 11.050(3) 27.772(10) 90.00 120.00 90.00 2936.8(16) 3 1.110 0.892 11060/3800 0.0566 0.0421/0.0502 0.0994/0.1012 0.941 0.05(3)

C52H44Co4N4O24 1344.63 295(2) triclinic P1̅ 6.404(3) 16.046(7) 25.698(11) 106.593(6) 96.038(6) 92.975(6) 2507.5(18) 2 1.781 1.398 13455/9565 0.0488 0.0707/0.1079 0.1578/0.1939 1.050

R1 = Σ||Fo| − |Fc||/Σ|Fo|; wR2 = [Σw(Fo2 − Fc2)2/Σw(Fo2)2]1/2.

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RESULTS AND DISCUSSION Synthesis. The formation of MOFs is significantly influenced by the reaction temperature, solvent, pH value, and so on. Initially, the solvothermal reaction of CoCl2 and H2cpna (molar ratio 1:1) in DMF/ethanol (4:6) solvents at 120 °C for 72 h gave a blue solution containing an unknown pink precipitate, which is an unstable dynamic product, that slowly changes into the stable thermodynamic product 1 at room temperature in two weeks. 1 can also be directly prepared by reacting Co(NO3)2 with H2cpna in DMF, DMF/ethanol, or DMA/ethanol solvents at 20−40 °C for three weeks. The change of the molar ratios of DMF/ethanol or the rise of the temperatures does not quicken the formation of 1, verifying the thermodynamic stability of 1. Comparably, 2 can be easily synthesized by reacting Co(NO3)2 with H2cpna in H2O containing NaOH or triethylamine at 120 °C. However, 2 is obtained with better purity at a higher yield in mixed DMA/ ethanol/water solvents. Crystal Structure of 1. Single-crystal X-ray crystallography reveals that 1 crystallizes in the space group P3121 and exhibits a non-interpenetrated 3D chiral framework based on the [Co2(O2C)2(μ2-H2O)(H2O)2] dimer. The asymmetric unit of 1 contains one Co2+ ion, one cpna2− ligand, one bridging H2O, and one terminal H2O ligand. The Co2+ ion is octahedrally coordinated by one pyridyl N atom and three carboxylate O atoms from four different cpna2−, and two H2O ligands (Figure 1a). Two Co2+ ions are combined by one bridging aqua O atom and two η1:η1:μ2 syn-syn carboxylate groups from two cpna2− to afford a [Co2(O2C)2(μ2-H2O)(H2O)2] dimer (Co···Co separation of 3.624 Å). The dimer has a C2 symmetry with the axis traversing the bridging aqua O atom and the center of two Co2+ ions. B



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Figure 1. (a) The coordination environment of Co2+ ions in 1. (b) The 2D sublayer structure in 1, indicating two kinds of vertical 21 heterochiral helical chains along the b axis and (210) direction.

In 1, the bridging fashion of cpna2− can be viewed as the combination of nicotiniate and benzoate units. The interlinkage between the nicotiniate units and Co2 dimers generates a 2D wrinkled grid layer parallel to the ab crystal face (Figure 1b). In the layer, two kinds of different 21 helical chains are formed along the b axis and (210) direction, which are vertical, and exhibit left-handed and right-handed chirality, respectively. Each layer is achiral, and it further joins the adjacent layers through benzoate units of cpna2− along the c axis, leading to a 3D framework (Figure 2). However, the overall framework is

dimers at the same time (Figures 2a and S2). In addition, a right-handed helical channel along the c axis is generated through the surrounding of three helical chains (Figures 2c and S3), which has a diameter of ca. 4.0 Å (excluding van der Waals radii of the atoms). The channels possess a 42.3% solvent accessible void,16 and their surfaces are decorated by aryl rings of cpna2− and Co2 coordination motifs. Crystal Structure of 2. Complex 2 crystallizes in the space group P1̅ and exhibits a dinuclear Co2-based non-interpenetrated 3D network. The asymmetric unit of 2 consists of four independent Co2+ ions, four cpna2−, and eight coordinated H2O molecules. As shown in Figure 3, all Co2+ ions show the

Figure 3. The coordination environment of Co2+ ions in 2.

similar octahedral coordination geometry, and each one is coordinated to one pyridyl N atom, one carboxylate O atom, and two carboxylate single bridging μ2-O atoms from four different cpna2− and two terminal H2O ligands. Co1 and Co2 or Co3 and Co4 are bridged by two carboxylate μ2-O atoms to form two similar [Co2(O2C)4(H2O)2] dimers with the Co···Co separations of 3.307 and 3.321 Å, respectively, and the Co···O···Co angles lying in the range 99.7(2)−100.6(2)°. The Co2 dimers are extended by carboxylate groups of cpna2− to generate a 2D achiral grid layer parallel to the (103) crystal face (Figure 4), in which the left-handed and right-handed helical chains are formed along the b axis. The neighboring

Figure 2. (a) The 31 helical (dark cyan) and zigzag (yellow) chains with the coshared Co2 dimers, (b) the 3D structure, and (c) the 1D helical channel along the c axis in 1.

chiral because the right-handed 31 helical chain is formed along the c axis by the carboxylate groups of cpna2− bridging Co2 dimers (Figure 2a), and the helical pitch is 27.772 Å. Moreover, this helix can be strengthened by the additional Co−O and Co−N bonds between Co2 and benzoate-pyridine units of other cpna2−, which shows a zigzag chain. Thereby the helix and zigzag chains are formed through the Co-shared Co2 C



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Figure 4. The 2D sublayer structure in 2 parallel to the (103) crystal face (a) and its simplified grid net (b).

Figure 5. (a) The (3,6)-connected anh net of 1 and 1D helix chain along the c axis, and (b) the (3,6)-connected rtl net of 2, which are based on the 2D layers in Figures S1 and 4b, respectively.

the best of our knowledge, the anh net is unknown in the previous MOFs. PXRD and Thermal Analysis. The PXRD patterns of the bulk samples of 1 and 2 match their simulated patterns from the single-crystal structures, showing the phase purity of the assynthesized products (Figures S7 and S8). TGA of 1 exhibits a significant weight loss of 26.0% from room temperature to 210 °C (Figure S9), implying the release of one DMF and nine H2O solvent molecules per formula unit (calc. 26.4%). Then a slow weight loss of 6.0% in the range 210−300 °C indicates the removal of the coordinated H2O molecules (calc. 6.1%), followed immediately by the framework collapse with an abrupt weight loss. For 2, the preliminary weight loss of 10.9% beginning at 130−270 °C corresponds to the removal of all H2O ligands (calc. 10.7%), then followed by a plateau of stability from 270 to 330 °C, whereupon the rapid dissociation of cpna2− induces the framework decomposition. Magnetic Property. The variable-temperature magnetic susceptibilities (χM) of 1 and 2 were examined in a 1000 Oe field in the range 1.8−300 K. As shown in Figures 6 and 7, at 300 K, the χMT values of each Co2 dimer for 1 and 2 are 5.74 and 6.65 cm3 K mol−1, respectively. These values are much higher than the value for two magnetically isolated spin-only S = 3/2 Co2+ systems (3.75 cm3 K mol−1), which is as expected because of the significant orbital contribution of high-spin Co2+ ion in an octahedral coordination environment. For 1, upon cooling, the χMT value declines monotonously and reaches 1.05 cm3 K mol−1 at 1.8 K, indicating a significantly antiferromagnetic exchange between the magnetic centers in Co2 dimer. The antiferromagnetic or ferromagnetic interaction for the Co(II)carboxylate dimers is closely related to the Co−O−Co exchange angles and Co···Co distances. In the Co2 unit of 1, the magnetic coupling between two Co2+ centers is transmitted

layers are further united by Co−N bonds involving Co2 dimers and the pyridyl rings of cpna2− along the a axis to afford a 3D framework (Figure S4). Such stacks lead to a 1D double chain generated by nicotiniate units of cpna2− and Co2 dimers along the a axis (Figure S5), being different from the situation in 1. Along the a axis, 2 exhibits a narrow channel arising from the eclipsed interlayer arrangements, which is fully occupied by the aqua ligands. Topological Analysis. Topologically, the cpna2− linker and Co2 dimer in 1 and 2 can be simplified as 3- and 6-connected nodes, respectively. Remarkably, the 6-connected Co2 nodes display significantly distorted trigonal-prism and octahedral environments in 1 and 2 (Figure S6), respectively. These nodes combine the distorted Y-shaped cpna2− ligand to form a binodal (3,6)-connected anh net for 1 with the point symbol of (4·62)2(44·62·88·10) (Figure 5a)17 and a (3,6)-connected rtl net for 2 with the point symbol of (4·62)2(42·610·83) (Figure 5b). Alternatively, both anh and rtl nets in 1 and 2 can be regarded as the assemblies of triangular cpna2− linking parallel 4connected 44 grid layers (Figures S1 and 4b).18 There are only six (3,6)-connected nets (anh, ant, apo, brk, pyr, rtl) that can be deconstructed into 2D layers linked by triangles, though more than 20 (3,6)-connected nets are documented in the RCSR database.7 The 2D layers in 1 and 2 are achiral. However, the layer along the b axis or (210) direction in 1 is chiral, which differs from the achiral character of the layer along any direction in 2. The difference results from the tetrahedral and square planar environments of the 4-connected centers in the layers of 1 and 2, respectively (Figures S1 and 4b), which leads to the two heterochiral vertical and parallel helical chains in their respective layers. Of note, the anh net is a hexagonal anatense (ant) framework,7a having the same point symbol as the ant net, but it exhibits different long vertex symbols.19 To D



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χCo =

12(A + 2)2 8Nβ 2 ⎡ 7(3 − A)2 x ⎢ + 5 25A k(T − θ )x ⎢⎣ ⎧ 2(11 − 2A)2 x 176(A + 2)2 ⎫ ⎬ +⎨ + 45 675A ⎩ ⎭ ⎧ (A + 5)2 x 20(A + 2)2 ⎫ ⎬x exp( −5Ax /2) + ⎨ − 9 27A ⎩ ⎭ ⎤ exp(− 4Ax)⎥ /[3 + 2 exp( −5Ax /2) + exp(− 4Ax)] ⎥⎦ (1)

where x = λ/kT, and A is a measure of the crystal field strength. The best fit for the magnetic susceptibility data gives the parameters λ = −125 cm−1, A = 1.12, and θ = −0.86 K for 1, and λ = −92 cm−1, A = 1.32, and θ = 5.85 K for 2 (Figures 6 and 7). The fitting θ values confirm the presence of antiferromagnetic and ferromagnetic intradimer exchanges for 1 and 2, respectively. Sorption Property. Immersing 1 in CH3OH for 72 h, the DMF molecules of crystallization in 1 were exchanged, which was confirmed by the disappearance of the strong DMF CO stretching peak at 1660 cm−1 in the IR spectrum of 1 after the solvent exchanging (Figure S10). In order to quantify the microporosity, the CH3OH-exchanged 1 was desolvated at 90 °C for 5 h under dynamic vacuum to yield a porous framework. The desolvated 1 displays the loss of crystalline phase, possibly due to the framework distortion stemming from the rotation between aryl rings and carboxylate groups or pyridyl and benzyl rings in cpna2−, as well as the geometric twist of metalcarboxylate units.23 The desolvated 1 shows a nonclassic type-I N2 sorption isotherm at 77 K, with the saturated sorption amount of ca. 13.8 cm3(STP) g−1 at 700 Torr (Figure 8). The obvious

Figure 6. Plots of the χM and χMT vs T for 1. Straight lines correspond to the best fit according to eq 1.

Figure 7. Plots of the χM and χMT vs T for 2. Straight lines correspond to the best fit according to eq 1.

through one μ2-Owater and two μ1,3-carboxylate bridges. The big Co−Owater−Co angle of 108.9(4)° and the long Co···Co distance of 3.624(1) Å are responsible for the antiferromagnetic interaction in 1, which is also found in other Co2-based complexes with μ1,3-carboxylate and μ2-Owater bridges.20 When the temperature decreases, the χMT of 2 decreases gradually with a distinct plateau (5.3 cm3 K mol−1) appearing below 25 K. Both the plateau of χMT from 25 to 8 K and the room temperature χMT (6.65 cm3 K mol−1) of 2 larger than that of 1 (5.74 cm3 K mol−1) suggest that the interaction of intradimer Co2+ centers is ferromagnetic, which is transmitted through two carboxylate single μ2-O bridges. The absence of an increase in the χMT curve of 2 at low temperature indicates that the ferromagnetic interaction is weak and possibly hidden by the spin−orbit coupling effect of Co2+ ions.21 The small Co−O− Co angles (99.7(2)−100.6(2)°), as well as short Co···Co distances (3.307 and 3.321 Å) are mainly responsible for the ferromagnetic property of 2. The ferromagnetic coupling has been observed in other Co2-based systems containing similar carboxylate single μ2-O bridges, which have the comparable Co···Co distances (3.17−3.32 Å) and Co−O−Co angles (92.5−100.7°).21b,22 The ground state for high-spin octahedral Co2+ is 4T1g and splits into a sextet, a quartet, and a Kramers doublet. The corresponding Hamiltonian is H = −λLS. The χM expression for 1 and 2 is provided in the following eq 1:

Figure 8. Gas sorption isotherms of 1 for N2 and CO2 at 77 and 295 K, respectively.

hysteretic desorption proves the microporous sorption character but not surface sorption because the desorption for the latter traces the adsorption process with almost no hysteresis.24 The hysteresis derives from the hindered escape of adsorbed N2 in the 1D narrow channel of 1.25 A classic typeI isotherm is observed for CO2 sorption at 195 K, with the sorption amount of 30.2 cm3(STP) g−1 at 760 Torr (Figure 8). The significant sorption selectivity of 1 for CO2 over N2 should be attributed to the smaller kinetic diameter of CO2 (3.30 Å) than N2 (3.64 Å), thereby CO2 molecules are able to diffuse E



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into the pore more easily. In addition, the large quadrupole moment of CO2 (4.30 × 10−26 esu−1 cm−1) compared with N2 (1.52 × 10−26 esu−1 cm−1) favors the strong CO2-framework interaction, so a higher CO2 uptake is available. Notably, the sorption amount of 1 for N2 and CO2 is much less than the estimated values from the crystal structure, which is probably caused by the structural distortion or the framework part disintegration after desolvation, being similar with the case in other porous MOFs.26 Treating the CH3OH-exchanged 1 at an elevated temperature (150 °C), the H2O ligand was removed. Disappointingly, this sample is nonadsorptive to N2 (77 K) or CO2 (195 K), implying the framework collapsed. This phenomenon is attributed to the prior escape of the bridging H2O ligand, since the Co−Owater bond of the bridging H2O ligand (2.237(3) Å) is longer than that of the terminal H2O ligand (2.149(3) Å).

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CONCLUSION In summary, we have successfully constructed two 3D (3,6)connected Co(II)-MOFs based on a new Y-shaped tridonal pyridyldicarboxylatic acid and different types of 6-connected Co2 dimers. The Co2 dimers exhibit distorted trigonal-prism and octahedral environments, which combine the asymmetric cpna2− triangles to generate anh and rtl nets for 1 and 2, respectively. 1 features a chiral framework with attractive 31 helical chains and channels. In 1 and 2, there are the similar achiral 2D grid layers which contain two 21 helical chains with opposite chirality and vertical or parallel arrangement, attributing to the tetrahedral and square planar coordination environments of 4-connected centers in the layers, respectively. Because of the different intradimer Co···Co separations and Co−O−Co angles, 1 and 2 show antiferromagnetic and weak ferromagnetic exchanges, respectively. In addition, 1 exhibits microporous sorption for N2 and CO2 at cryogenic temperatures.

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ASSOCIATED CONTENT

* Supporting Information S

Crystallographic information file (CIF), PXRD, TGA, FTIR, additional molecule figures, bond length/angle and hydrogen bonds tables. This information is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for financial support from the NSF of China (Grants 20771090, 21001088, 20931005 and 91022004), the Doctoral Program of Higher Education of China (Grant 20096101110005), China Postdoctoral Scientific Foundation (Grant 20100471627), and NSF of Shaanxi, China (Grants 2009JZ001 and 2010JK872).

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REFERENCES

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Two New (3,6)-Connected Frameworks Based on an Unsymmetrical

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